It's an outdated misnomer, originally associated with the belief that this was a period of scientific and technological stagnation. Today it is recognised that the "Dark Ages" were not so backward after all.

Well it was a dark age because of the end of the political unity that was the Roman empire. Otherwise, things are not that clear : the economy of the empire was already weakened long before its end. And actually, for many countries, the dark ages were much better than the ancient period. For example, Germany in 1000 was already much more developped than in, say, 200 AD.

The other trend associated with the darks ages was desurbanization. However, it ought not to be exagerrated. Overall, the Roman empire was highly urbanized, but it was not uniform. Italy indeed became much less urbanized during the dark ages, but for most of Gaul (except the southeast) or Britain, it was not that clear.

For the orient too, it wasn't dark at all. The Byzantine empire had its ups and downs but it was always impressive, rich and magnificent. And more oriental regions became involved in the islamic golden age.

As above, the term is hardly accurate and a misnomer. It is no longer used seriously by historians. But it does till survive in popular culture and peception. Such things take time to change, ideas and notions have to filter down from academics to the masses. So the term will probably be used for quite a while in general.

It wasnt a dark age, but it was perhap a bit darker than before and after it. But as pointed out above such terminology is never that simple.

its a term that was coined during the early modern era, 17th or 18th century, to describes the years between them and the roman empire which at the time was looked back with great admiration. they saw the years after it as a fall from grace as the world fell apart only for them to them bring things back as modern nation states began to rise. its not a term that describes the era well and we know now that it wasn't as 'dark' as it was made out to be.

The era was called the "Dark Ages" also because we don't have a lot of written sources from that time period, especially from the early part of the dark ages (500 to 800 CE). Since until recently, most historians only had written sources to rely on, those ages were considered "Dark". In a similar way, Africa was called the "Dark Continent". There was not a lot of knowledge available to Europeans about Africa south of the Sahara, hence the use of the term "Dark Continent".